The present invention relates generally to a lenslet array and more particularly to a lenslet arrangement such as is found in my copending application Ser. No. 912,688, filed June 5, 1978 now U.S. Pat. No. 4,185,191 and in the copending application of Stauffer and Wilwerding, Ser. No. 16,595, filed Mar. 1, 1979 wherein the lenslets are used in connection with distance determining or automatic focusing of, for example, photographic or television cameras.
In the above-mentioned copending applications, radiation from a remote scene to be focused upon is directed by an objective lens to a plurality of lenslets mounted proximate the image plane of the objective lens. Each lenslet produces an image of the exit pupil of the objective lens and proximate the image plane of each lenslet is mounted a pair of radiation sensitive detectors. Each detector produces an output indicative of the radiation it receives and when the objective lens is properly positioned in the desired focus position, the detectors in each pair will receive approximately the same amount of radiation. As the objective lens moves from a proper focus position, the output of the detectors becomes unequal. The inequality in the outputs of the detectors is analyzed by a system to determine the direction the objective lens must be moved to attain a proper focus.
Lenslets which are positioned near the center of the lenslet array generally receive radiation from the objective lens approximately equally about the optic axis of such lenslets so that the radiation they transmit to the detectors emerges generally along their optic axes. It has been found, however, that lenslets near the edge of the lenslet array receive radiation from the objective lens at an angle to the optic axis of such lenslets so that the radiation transmitted by such lenslet travels along a path which exposes one of the detectors in the pair to a greater share of the radiation than the other of the detectors of that pair even when the objective lens is in the proper focus position and thus the output of the two detectors may not be equal which could falsely indicate an out-of-focus condition.
SUMMARY OF THE INVENTION
The present invention overcomes the problem found in the prior art by introducing a corrector lens between the objective lens and the lenslet array so as to direct the radiation from the objective lens to the individual lenslets more nearly parallel to and symmetric about the optic axis of each lenslet and thus provide an image from each lenslet which emerges generally symmetrically about its optic axis. The two detectors may now be mounted substantially equal distant from the optic axis of each lenslet and thus receive substantially the same amount of radiation when the objective lens is in the proper focus position.